In recent years, various stem cells and many methods of inducing their differentiation into somatic cells have been discovered, and therefore tissue engineering has been intensively focused as a novel medical treatment that takes the place of organ transplantation. This technology aims at in vivo or in vitro construction of organs directly used for treatments of humans, and the technology has realized many techniques of expressing organ-like functions in vitro. Thus, the technology is expected to provide high throughput (HTS) cell evaluation systems that can be used for pharmacological experiments without preparation of organs, per se, and can cope with an enormous number of tests in researches for drug design, diagnosis and the like. Further, the technology is also expected as a novel technology that enables substance production unique to mammalian cells.
Analysis of human DNA nucleotide sequences by the human genome project has been almost completed, and researches in this field have been moving to post-genomic researches using that information. An example is a tailor-made medicament, which is a frequent article on recent newspaper. The researches are expected to yield enormous markets of medicaments, and support tools for drug design and medication. DNA chips and protein chips have been currently focused as such tools, and many companies including American venture business entities are in fierce competition.
However, the number of the human genes reported by the human genome project is about 30,000 to 40,000, which is not so larger compared with the number of 13,000 in fly, and there are also many homologous genes over species. Therefore, it has been becoming clear that individuality of species cannot be determined solely based on DNA. Human genetic information is used for cell construction starting from DNA via RNA to proteins in accordance with the central dogma. Transmission of the information is not one-way, but consists of a nonlinear system including many interactions and feedback systems, i.e., a so-called complex system. In life entities, there is a mechanism imparting stability and robustness thereto. For example, in the liver, a different expression system will function depending on a state of fasting, satiety, and drinking, although a gene, cells and tissues are identical. Therefore, in order to elucidate life phenomena, it is attempted to understand a life entity as a system, not merely to focus on molecular reactions, and study by simulation on the basis of boundary conditions that can be obtained by analyzing cells and organs in vivo. This new technical field is called a bio-system engineering, which has rapidly been focused.
In order to accurately understand life phenomena, it is necessary to handle systems of at least a cellular level or higher, and for this purpose, a tool is desired in which cells or tissues are arrayed while their native functions are maintained. Thus, researches for methods of constructing cell arrays have become active. Specifically, methods of controlling hydrophilicity or hydrophobicity of a surface of solid substrate such as glass substrate by using lithography are known (S. N. Bhatia et al, Biotecnol. Prog., 14, 378 (1998); Toshihiro Akaike et al., Japanese Patent Unexamined Publication (KOKAI) No. 5-176753; Otsuka et al, 30th Biomedical Polymer Symposium, Lecture Summaries, page 9 (2001); Kikuchi et al, 30th Biomedical Polymer Symposium, Lecture Summaries, page 35 (2001) and the like). However, these methods require expensive apparatuses for lithography, and also have a problem in that carriers for cell culture cannot be prepared conveniently.
A water-containing polymer gel has a structure similar to that of a living body, and has a property of expanding or shrinking depending on external conditions such as temperature, acidity, and alkalinity. Accordingly, applications in the medical field, including a use as an artificial organ or tissue such as an artificial muscle or encapsulation of a drug therein to control an amount to be released, have been attempted, as well as applications as an anchorage of cell growth in a cell culture as a gel containing various kinds of cytokines and the like.
It is known that cells are arrayed with polarity when they form a tissue in a living body. For example, hepatocytes absorb blood components from the vascular endothelial cell side, and excrete metabolites such as bile acid from the opposite side. Since this bile acid has potent cytotoxicity, cell culture by adhering the cells on an impermeable support such as glass suffers from a problem that stable long-term culture is difficult. Although it is known that the polarity of cells is expressed by stimulation given from one way to the cells, cell culture by adhering the cells on an impermeable support raises a problem that stimulation cannot be given from the adhesion side. Further, in order to perform lithography, a photosensitive solution needs to be applied beforehand. However, a substance-permeable support will cause a problem that the photosensitive solution as well as reaction products and developing/fixing solutions permeate into the support, and toxicity or stimulation is given to cultured cells due to denaturation of the support, remaining of compounds in the support or the like.
To solve these problems, a permeable collagen membrane for cell culture, MEN-01, is sold by KOKEN CO., LTD. as a cell culture material for culturing cells with different media for the both sides of the cells. However, in this cell culture material, the collagen membrane is much swelled with a medium, and thus the material is significantly distorted during the culture. Therefore, it is difficult to observe a culture state of cells. In Japanese Patent Unexamined Publication (KOKAI) No. 2001-120267, a carrier for cell culture is proposed which comprises a porous membrane together with an alginic acid gel layer and an extracellular matrix component gel layer or an extracellular matrix component sponge layer which are laminated on the porous membrane. However, this carrier for cell culture has a microfilter layer, and therefore, growth state of cells cannot be observed under an optical microscope.